Project Summary: The influx of Ca through L-type Ca channels in surface membrane of cardiomyocytes regulates a variety of cellular processes including contraction, secretion, cell signaling, and gene expression. The long-term goals of this research are 1) to discriminate between distinct populations of L-type Ca channels in cardiomyocytes based on the unique macromolecular complex of associated proteins;2) to determine how these different populations of channels specifically contribute to various Ca-regulated cellular processes;and 3) to understand how alterations in the different populations of Ca channels contribute to cardiovascular disease. These goals will be approached initially focusing on Cav1.2 L-type Ca channels localized to the specialized membrane microdomains known as caveolae which are defined by the signature protein caveolin-3 (Cav-3). The contribution of Cav1.2 channels to the genesis of the long QT syndrome associated with recently identified mutations in Cav-3 will be defined. Using immunoprecipitation techniques, GST-Cav-3 pull-down, immunoconfocal microscopy, immunogold electron microscopy, siRNA knockdown of targeted proteins, heterologous expression of Cav1.2 channels and key associate proteins, and conditional knockout of Cav-3 in mice, we will address three specific aims: 1) Define the relative abundance and composition of the Cav1.2 channels localized to caveolae in ventricular myocytes;2) Determine if Cav-3 and associated core scaffolding proteins are essential for normal basal L-type Ca current and its ([unreadable]-AR regulation in ventricular myocytes;3) Determine the impact of long QT-related Cav-3 genetic mutations on Cav1.2 L- type Ca channels. Relevance: These studies will provide molecular definition of the subpopulation of Ca channel proteins localized to caveolae and thus offer mechanistic insights into the genesis of the long QT syndrome and life-threatening arrhythmias associated with mutations in the signature protein of caveolae in the heart, caveolin-3. Furthermore, this research will impact our understanding of heart failure and atrial fibrillation given that alterations in caveolae and Ca channels have been detected in these diseases. Ultimately, a molecular understanding of caveolae and L-type Ca2+ channels has the potential to inspire new therapies for these prevalent cardiovascular diseases.